<img id="pic" onclick="kaiDeng()" src="pic_bulboff.gif" />

<script>
var i =1;

function kaiDeng(){
    if(i==1){
       pic.src = "pic_bulbon.gif";
       i = 0;
   }else{
    pic.src = "pic_bulboff.gif";
      i = 1;
  }
}
</script>